The following information describes one of the many possible environments in which the invention can be used. It is provided to assist the reader to understand the invention, as novel material is often more readily understood if described in a familiar context.
Magnetic resonance imaging (MRI) is a noninvasive method of producing high quality images of the interior of the human body. It allows medical personnel to see inside the body (e.g., organs, muscles, nerves, bones, and other structures) without surgery or the use of potentially harmful ionizing radiation such as X-rays. The images are of such high resolution that disease and other forms of pathology can often be visually distinguished from healthy tissue. Magnetic resonance (MR) systems and techniques have also been developed for performing spectroscopic analyses by which the chemical content of tissue or other material can be ascertained.
MR imaging and spectroscopic procedures are performed in what is known as an MR suite. As shown in FIG. 1A, an MR suite typically has three rooms: a scanner room 1, a control room 2, and an equipment room 3. The scanner room 1 houses the MR scanner 10 into which a patient is moved via a slideable table 11 to undergo a scanning procedure, and the control room 2 contains a computer console 20 from which the operator controls the overall operation of the MR system. In addition to a door 4, a window 5 is typically set in the wall separating the scanner and control rooms to allow the operator to observe the patient during such procedures. The equipment room 3 contains the various subsystems necessary to operate the MR system. The equipment includes a power gradient controller 31, a radio frequency (RF) assembly 32, a spectrometer 33, and a cooling subsystem 34 with which to avoid the build up of heat which, if left unaddressed, could otherwise interfere with the overall performance of the MR system. These subsystems are typically housed in separate cabinets, and are supplied electricity through a power distribution panel 12 as are the scanner 10 and the slideable patient table 11.
An MR system obtains such detailed images and spectroscopic results by taking advantage of a basic property of the hydrogen atom, which is found in abundance in all cells within the body. Within the body's cells, the nuclei of hydrogen atoms naturally spin like a top, or precess, randomly in every direction. When subject to a strong magnetic field, however, the spin-axes of the hydrogen nuclei align themselves in the direction of that field. This is because the nucleus of the hydrogen atom has what is referred to as a large magnetic moment, which is basically an inherent tendency to line up with the direction of the magnetic field to which it is exposed. During an MR scan, the entire body or even just one region thereof is exposed to such a magnetic field. This causes the hydrogen nuclei of the exposed region(s) to line up—and collectively form an average vector of magnetization—in the direction of that magnetic field.
As shown in FIGS. 1B and 1C, the scanner 10 is comprised of a main magnet 101, three gradient coils 103a-c, and, usually, an RF antenna 104 (often referred to as the whole body coil). Superconducting in nature, the main magnet 101 is typically cylindrical in shape. Within its cylindrical bore, the main magnet 101 generates a strong magnetic field, often referred to as the B0 or main magnetic field, which is both uniform and static (non-varying). For a scanning procedure to be performed, the patient must be moved into this cylindrical bore, typically while supine on table 11, as best shown in FIGS. 1B and 1C. The main magnetic field is oriented along the longitudinal axis of the bore, referred to as the z direction, which compels the magnetization vectors of the hydrogen nuclei in the body to align themselves in that direction. In this alignment, the hydrogen nuclei are prepared to receive RF energy of the appropriate frequency from RF coil 104. This frequency is known as the Larmor frequency and is governed by the equation ω=YB0, where ω is the Larmor frequency (at which the hydrogen atoms precess), Y is the gyromagnetic constant, and B0 is the strength of the main magnetic field.
The RF coil 104 is generally used both to transmit pulses of RF energy and to receive the resulting magnetic resonance (MR) signals induced thereby in the hydrogen nuclei. Specifically, during its transmit cycle, the coil 104 broadcasts RF energy into the cylindrical bore. This RF energy creates a radio frequency magnetic field, also known as the RF B1 field, whose magnetic field lines point in a direction perpendicular to the magnetization vectors of the hydrogen nuclei. The RF pulse (or B1 field) causes the spin-axes of the hydrogen nuclei to tilt with respect to the main (B0) magnetic field, thus causing the net magnetization vectors to deviate from the z direction by a certain angle. The RF pulse, however, will affect only those hydrogen nuclei that are precessing about their axes at the frequency of the RF pulse. In other words, only the nuclei that “resonate” at that frequency will be affected, and such resonance is achieved in conjunction with the operation of the three gradient coils 103a-c.
Each of the three gradient coils is used to vary the main (B0) magnetic field linearly along only one of the three spatial directions (x,y,z) within the cylindrical bore. Positioned inside the main magnet as shown in FIG. 1C, the gradient coils 103a-c are able to alter the main magnetic field on a very local level when they are turned on and off very rapidly in a specific manner. Thus, in conjunction with the main magnet 101, the gradient coils can be operated according to various imaging techniques so that the hydrogen nuclei—at any given point or in any given strip, slice or unit of volume—will be able to achieve resonance when an RF pulse of the appropriate frequency is applied. In response to the RF pulse, the precessing hydrogen nuclei in the selected region absorb the RF energy being transmitted from RF coil 104, thus forcing the magnetization vectors thereof to tilt away from the direction of the main (B0) magnetic field. When the RF coil 104 is turned off, the hydrogen nuclei begin to release the RF energy they just absorbed in the form of magnetic resonance (MR) signals, as explained further below.
One well known technique that can be used to obtain images is referred to as the spin echo imaging technique. Operating according to this technique, the MR system first activates one gradient coil 103a to set up a magnetic field gradient along the z-axis. This is called the “slice select gradient,” and it is set up when the RF pulse is applied and is shut off when the RF pulse is turned off. It allows resonance to occur only within those hydrogen nuclei located within a slice of the region being imaged. No resonance will occur in any tissue located on either side of the plane of interest. Immediately after the RF pulse ceases, all of the nuclei in the activated slice are “in phase,” i.e., their magnetization vectors all point in the same direction. Left to their own devices, the net magnetization vectors of all the hydrogen nuclei in the slice would relax, thus realigning with the z direction. Instead, however, the second gradient coil 103b is briefly activated to create a magnetic field gradient along the y-axis. This is called the “phase encoding gradient.” It causes the magnetization vectors of the nuclei within the slice to point, as one moves between the weakest and strongest ends of this gradient, in increasingly different directions. Next, after the RF pulse, slice select gradient and phase encoding gradient have been turned off, the third gradient coil 103c is briefly activated to create a gradient along the x-axis. This is called the “frequency encoding gradient” or “read out gradient,” as it is only applied when the MR signal is ultimately measured. It causes the relaxing magnetization vectors to be differentially re-excited, so that the nuclei near the low end of that gradient begin to precess at a faster rate, and those at the high end pick up even more speed. When these nuclei relax again, the fastest ones (those which were at the high end of the gradient) will emit the highest frequency of radio waves and the slowest ones emit the lowest frequencies.
The gradient coils 103a-c therefore allow these radio waves to be spatially encoded, so that each portion of the region being imaged is uniquely defined by the frequency and phase of its resonance signal. In particular, as the hydrogen nuclei relax, each becomes a miniature radio transmitter, giving out a characteristic pulse that changes over time, depending on the local microenvironment in which it resides. For example, hydrogen nuclei in fats have a different microenvironment than do those in water, and thus emit different pulses. Due to these differences, in conjunction with the different water-to-fat ratios of different tissues, different tissues emit radio signals of different frequencies. During its receive cycle, RF coil 104 detects these miniature radio emissions, which are often collectively referred to as the MR signal(s). From the RF coil 104, these unique resonance signals are conveyed to the receivers of the MR system where they are converted into mathematical data. The entire procedure must be repeated multiple times to form an image with a good signal-to-noise ratio (SNR). Using multidimensional Fourier transformations, the MR system then converts the mathematical data into a two- or even a three-dimensional image of the body, or region thereof, that was scanned.
As shown partially in FIG. 1A, the scanner room 1 is shielded to prevent the entry and exit of electromagnetic waves. Specifically, the materials and design of its ceiling, floor, walls, door, and window effectively form a barrier or shield 6 that prevents the electromagnetic signals generated during a scanning procedure (e.g., the RF energy) from leaking out of scanner room 1. Likewise, shield 6 is designed to prevent external electromagnetic noise from leaking into the scanner room 1. The shield 6 is typically composed of a copper sheet material or some other suitable conductive layer. The window 5, however, is typically formed by sandwiching a wire mesh material between sheets of glass or by coating the window with a thin layer of conductive material to maintain the continuity of the shield. The conductive layer also extends to the door 4, which when open allows access to the scanner room 1 and yet when closed is grounded to and constitutes a part of shield 6. The ceiling, floor, walls and door of shield 6 provide approximately 100 decibels (dB) of attenuation, and window 5 approximately 80 dB, for the typical operating range of MR scanners (˜20 to 200 MHz). Barrier 6 thus shields the critical components (e.g., scanner, preamplifiers, receivers, local coils, etc.) of the MR system from undesirable sources of electromagnetic radiation (e.g., radio signals, television signals, and other electromagnetic noise present in the local environment).
The shield 6 serves to prevent external electromagnetic noise from interfering with the operation of the scanner 10, which if not addressed could otherwise result in degradation of the images and/or spectroscopic results obtained during the scanning procedures. For the scanner 10 to operate, however, the shield 6 must still allow communication of data and control signals between the scanner room 1 and the control and equipment rooms 2 and 3, and such communication is generally accomplished through a penetration panel 16.
As shown in FIG. 1A, the penetration panel 16 is typically incorporated into the wall between the scanner and equipment rooms 1 and 3. It features several ports through which the scanner 10 and other devices in the scanner room 1 are connected by cables to the computer console 20 and control subsystems in the control and equipment rooms 2 and 3, respectively. Each port typically includes a filtered BNC connector, which allows the communication of data and/or control signals while still maintaining the barrier to unwanted electromagnetic signals.
Several auxiliary systems designed for use in the MR suite require communication across the shield 6. These systems are typically bifurcated, i.e., they have two pieces of equipment, with one piece located in the scanner room 1 and the other situated in the control room 2. One example is the Spectris® MR Injector System produced by Medrad, Inc., of Indianola, Pa. It allows contrast media to be injected into the blood stream of a patient undergoing an MR procedure. (As is well known, contrast media serves to increase the contrast between the different types of tissues in the region of the body undergoing a scan, and thereby enhances the resolution of the images obtained during the scan.) In this bifurcated system, an injection control unit in the scanner room 1 with which to inject the contrast media into the patient requires communication with a controller therefor situated in the control room 2. This is disclosed in U.S. Pat. No. 5,494,036 to Uber, III et al., incorporated herein by reference. The '036 patent discloses that the injection control unit and its controller communicate across shield 6 using a pair of transceivers attached to, and aimed at each other through, opposite sides of window 5. They allow the injection control unit and controller to communicate, via the transceivers and their associated fiber optic cables, at frequencies (e.g., infrared or visual) that readily penetrate the shield 6 yet do not adversely affect the operation of the MR system.
The Spectris® Solaris™ MR Injector System, which is also produced by Medrad, Inc., uses a fiber optic link only, without resort to transceivers, to convey its data and control signals across the barrier 6. As shown in FIG. 2, this injector system has its fiber optic cable 13 routed through the shield 6 (i.e., preferably through one of the tuned ports in penetration panel 16) to enable optical communication between its injection control unit 50 and its controller 60. Because the communications links of the aforementioned injector systems are implemented optically, they do not introduce any potentially troublesome RF interference into the scanner room 1 as would be the case if standard wire cabling were used.
More relevant to the invention disclosed below, several prior art injector systems use batteries to supply power to their injection control units rather than AC power. One disadvantage of running AC power cords in the scanner room 1, particularly if close to the scanner 10, is that unless heavily shielded they tend to radiate RF emissions, which can interfere with the operation of the scanner 10 and cause artifacts to appear in the resulting images. The Spectris® Solaris™ MR Injector System, for example, as shown in FIG. 2, has its injection control unit 50 powered with a battery pack 40 that plugs into a corresponding socket 52 within the lower console housing 51. The battery pack 40 is rechargeable through use of a separate battery charger 41, as shown in FIG. 3.
Although it reduces the likelihood of tripping accidents due to the absence of power cords in the scanner room 1, the use of a stand-alone battery pack still poses several disadvantages to the operators of injector systems so equipped. First, the operator must regularly monitor the state of charge of the battery packs, which can generally be done in conjunction with most injector systems. If a battery pack with a low state of charge is not detected in a timely fashion, however, the scanning procedure will have to be delayed while the depleted battery pack in the injection control unit is swapped for a fully-charged one from the battery charger. At hospitals and other sites that routinely perform high numbers of contrast-enhanced procedures, such delays are particularly burdensome, as the battery packs must be swapped relatively often. Such delays inevitably reduce the number of patients that can be scanned in any given time period. This not only decreases the amount of revenue that can be derived from the MR suite but also ultimately imposes greater overall costs on the providers, and hence users, of medical services.
The Optistar™ Injector System, produced by the Liebel-Flarsheim Company of Mallinckrodt Inc., a division of Tyco International Ltd., attempts to overcome these disadvantages by routing DC power from the control or equipment rooms 2 and 3 through penetration panel 16 into the scanner room 1. As disclosed in U.S. Patent Application Publication No. 2002/0169415, situated in the control room is a power supply, which has an off-the-shelf AC/DC converter and a standard data link incorporated into one box. At its input, the AC/DC converter plugs into either a 115v AC outlet or a 240v AC outlet. An RF shielded cable from the power supply box routes power conductors (which carry DC power from the output of the AC/DC converter) and data conductors (which carry data and control signals to and from the computer console) through the penetration panel into the scanner room. The power conductors are connected directly to existing wiring within the battery compartment of the injection control unit, thereby eliminating the need for batteries which were necessary to operate an earlier pre-power supply version of the Optistar™ Injector System. In the Optistar™ Service and Parts Manual 801993-A (April 2001) with amended Installation Instructions 801995-A (May 2001), the power supply box is shown deployed in either the control room or the equipment room.
The advantage of such a power supply scheme is that heavy users of such injector systems do not have to contend with the task of swapping batteries. Although this scheme provides an uninterrupted supply of DC power to the injection control unit, it denies the user the increased mobility that an injection control unit has in the scanner room when powered by batteries. This shortcoming is but one of several that the Liebel-Flarsheim power supply scheme exhibits when compared to the invention disclosed below. The advantages of the invention herein presented will become fully apparent to persons skilled in the relevant art from a reading of the detailed description section of this document, and will become particularly apparent when the detailed description is considered along with the drawings and claims presented herein.